In recent years, large-scale data center environments or virtual machine environments thereon have increasingly been used. With this increase, SDNs (Software-Defined Networks) have been configured on such virtual machine environments. In such cases, since a VLAN (Virtual Local Area Network) or the like has problems that partitioning resources of network apparatuses are small and settings of network nodes are complex, an overlay network technique for configuring an edge overlay network is used.
Examples of the edge overlay network technique include tunneling techniques such as a VXLAN (Virtual eXtensible Local Area Network) and NVGRE (Network Virtualization using Generic Routing Encapsulation) is used (see Non Patent Literatures (NPLs) 1 and 2). In these techniques, communications on a virtual network configured on virtual machines are encapsulated and forwarded to a substrate network (physical network) configured by network nodes configuring the virtual machine environment. In these tunneling techniques, it is possible to virtually increase the virtual-network partitioning resources by adding virtual network IDs when encapsulation is performed. In addition, in these tunneling techniques, burden required for settings of network nodes is reduced by using communications on the substrate network.
However, in these tunneling techniques, processing about broadcast, multicast, and unknown unicast is not specifically defined. It is only defined that an IP (Internet Protocol) multicast technique on the substrate network is used. While an IP multicast address could be shared, an IP multicast address is normally set per virtual network ID, and forwarding is achieved throughout the network of the virtual machine environment configured, namely, throughout the target virtual network (see “4.2. Broadcast Communication and Mapping to Multicast” in NPL 1 and “4.1. Broadcast and Multicast Traffic” in NPL 2).
PTL 1 discloses a switch that encapsulates a packet by using a header called a TRILL (Transparent Interconnection of Lots of Links) header. According to Patent Literature (PTL) 1, this switch comprises: a determining mechanism configured to determine an internal multicast group identifier based on a source address, a multicast address, and a multicast tree identifier field associated with a multicast packet; and a forwarding mechanism configured to forward the multicast packet based on the internal multicast group identifier.
NPL 3 is a white paper on a network control technique called OpenFlow. By using OpenFlow, an OpenFlow switch is allowed to function as a TEP apparatus in a tunneling technique.
PTL 1: Japanese Patent Kohyo Publication No. 2013-528340A
NPL 1: M. Mahalingam, and seven others, “VXLAN: A Framework for Overlaying Virtualized Layer 2 Networks over Layer 3 Network,” [online], [searched on Nov. 11, 2013], Internet <URL:http://tools.ietf.org/pdf/draft-mahalingam-dutt-dcops-vxlan-02.pdf>
NPL 2: M. Sridharan, and nine others, “NVGRE: Network Virtualization using Generic Routing Encapsulation,” [online], [searched on Nov. 11, 2013], Internet <URL:http://tools.ietf.org/pdf/draft-sridharan-virtualization-nvgre-01.pdf>
NPL 3: Nick McKeown, and seven others, “OpenFlow: Enabling Innovation in Campus Networks,” [online], [searched on Nov. 11, 2013], Internet <URL:http://www.openflow.org/documents/openflow-wp-latest.pdf>